If you're going as a guest of the main sponsor, then the men hosting will probably be either in suits or slightly more casual trousers with jackets/blazers and shirts, probably without ties (depending on the weather). The women will probably be in dresses/skirts and tops with a jacket, again depending on the weather.
As rubybleu says, if it's warm, the tent can get a bit stuffy - there is air con, but it doesn't reach the whole space (it's massive!). There is a balcony round the outside where you can get a bit of fresh air and see the show from a different angle. There is seating in the tent, so your feet can get a bit of a rest.
Also, there is a cloakroom, where you can leave coats, bags etc, so you could always wear some trainers for wandering round the show and then swap for smarter shoes when you're in the tent itself.
I think you could wear ballet pumps/loafers with those trousers, and a nice top/scarf/jacket combo would be perfect.
Btw if you are in the main sponsor's tent, you are very lucky! It's always beautifully designed, the food is fab and (most importantly!) there are nice loos
. Have fun!